The invention relates to a tube having a throttle insert, to a throttle insert and to a method for producing a tube.
In numerous fields of use, it is necessary for liquids to be dispensed or dosed in dropwise fashion. This applies in particular to liquids with pharmaceutical or cosmetic active substances or for liquids with coloring agents, flavoring agents or aromatic substances, which are used for example in the processing of foodstuffs. The viscosity of such liquids preferably lies in the range from 1 to 100 MPa·s. The term “liquids” also refers to liquid mixtures and emulsions.
Suitable vessels for storing and dispensing such liquids are in particular tubes and small tube-like bottles. These comprise a reservoir, which contains the liquid to be dispensed, and a connector with a dispensing opening. The connector forms a dispensing duct, the distal end of which is connected to the reservoir and at the proximal end of which the dispensing opening is arranged. The expressions “proximal” and “distal” relate in each case to the position or direction relative to the dispensing opening. Various factors influence the size and/or the volume of droplets formed by the liquid at the dispensing opening before said droplets detach from the connector. Such factors are for example the interfacial tension or the surface tensions of the liquid to be dispensed and of the connector, the size and shape of the connector in the region of the dispensing opening, the pressure and the flow speed of the liquid in the dispensing duct, and the gravitational force acting on the emerging liquid.
In particular in the case of tubes or tube-like vessels whose reservoir is delimited by a deformable shell, a pressure force acting on the respective tube from the outside in addition to the ambient pressure gives rise to a pressure increase in the interior of the reservoir in relation to the ambient pressure. In this way, liquid is forced out of the reservoir through the dispensing duct to the dispensing opening, where said liquid emerges from the tube. With increasing pressure, the volume flow of the liquid discharged through the dispensing opening also increases. This dependency of the volume flow on the pressure force exerted on the tube by a person in addition to the ambient pressure prevents or hinders the formation of droplets of uniform size. Dosing of the liquid through the dispensing of droplets of uniform size is thereby impaired or even made impossible.
In the case of tubes whose shell is elastically deformable, wherein the shell may be manufactured for example from plastic or from a composite material with plastic, the elastic restoring force of the material in the absence of forces acting on the shell from the outside in addition to the ambient pressure has the effect that the pressure in the reservoir is lower than the ambient pressure. In the presence of an adequately large pressure difference, this has the effect that liquid situated in the dispensing duct is forced by the suction action back into the reservoir, wherein ambient air ingresses into the dispensing duct through the dispensing opening.
WO2013/075256A1 has disclosed a tube which comprises a dispensing duct in the form of an elongate connector. The distal end of the connector is connected via a tube shoulder to the tube shell. The connector is, on the outside and on the inside, of slightly conical form, wherein the inner diameter decreases from the distal end to the dispensing opening. Proceeding from the distal end of the connector, an insert is inserted into the connector such that an abutment element of the insert abuts against the inner side of the tube shoulder and thereby prevents the insert from ingressing further into the connector in the direction of the dispensing opening. The insert comprises a proximal section and a distal section, the shell surfaces of which bear in sealing fashion against the inner wall of the connector in said position. The two sections of the insert are connected to one another by a connecting neck of relatively small diameter, such that the inner side of the tubular connector and the insert delimit a ring-shaped intermediate space. The intermediate space is connected by in each case one longitudinal groove in the distal section and in the proximal section of the insert to the interior of the tube body and to that section of the dispensing duct which adjoins the dispensing opening. An additional recess in the abutment element ensures that the connection to the interior of the tube body is ensured. In this way, a throttle passage is formed which acts as a flow resistance and which limits the volume flow of the liquid to be dispensed even if the tube is compressed. It is thereby ensured that the formation of droplets at the dispensing opening is substantially independent of the pressure force exerted on the tube.
The insert comprises, axially adjoining the abutment element in the distal direction, a projection which can be utilized as an installation aid for the insertion of the insert into the connector. This projection is formed coaxially and mirror-symmetrically with respect to the front part of the insert, wherein the plane of symmetry lies in the region of the abutment element.
The projection protrudes into the tube body to a relatively great extent. When the flexible tube shell is compressed, said tube shell can come into contact with the projection and exert a force on the insert. This can cause a release of the force-fitting connection between the shell surfaces of the insert and the inner wall of the connector.
In the case of a tube as disclosed in WO2013/075256A1, the insert and the connector are of conical form and are precisely coordinated with one another in terms of shape and size. In a relative axial position defined by the abutment element and the tube shoulder, it is necessary for the shell surfaces of the insert to bear areally in sealing fashion against the inner wall of the connector with the exertion of a radial pressing force. This necessitates an adequately large length of the connector and of the insert in the axial direction. WO2013/075256A1 discloses that the connector is in the form of an elongate cannula and comprises a section with an external thread, which adjoins the tube shoulder, and a front section, which adjoins the former section and which has the dispensing opening. The insert extends in the axial direction beyond the section with the external thread into the front section. The diameter of the dispensing duct, even at the distal end of the connector, is small in relation to the length of the connector.